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Old 05-12-2010, 06:26 AM   #1
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Fan tripping GFCI


I have a gfci-protected bathroom fan in my shower enclosure. When I turn it on and off, but move the switch slowly, it trips the gfci when the switch is just turning from on to off or vice versa. If I flip the switch quickly it doesn't trip. Any idea what that might be?
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Old 05-12-2010, 07:13 AM   #2
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If you move the switch handle slowly, you get a bigger spark at the switch contacts inside, although I do not see why this shoulld trip a GFCI.
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Old 05-12-2010, 07:18 AM   #3
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Quote:
Originally Posted by AllanJ View Post
If you move the switch handle slowly, you get a bigger spark at the switch contacts inside, although I do not see why this shoulld trip a GFCI.
Yeah, maybe an AFCI...

The switch is a double-switch. The bottom half controls the shower light, which doesn't appear to trip anything.

I did all the wiring for my 2 bathrooms myself, except connecting the fan. I ran the wires right to the fan, then the contractor who is building it for me connected the wiring after running the duct (I wasn;t home).I can't imagine he messed up connecting 2 wire-nuts. even so....that would have nothing to do with the switch, right?
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Old 05-12-2010, 10:10 AM   #4
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Quote:
Originally Posted by secutanudu View Post
If I flip the switch quickly it doesn't trip. Any idea what that might be?
You need a new switch.
If the hysteresis in the switch is working it wouldn't allow so-called 'teasing'.
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Old 05-12-2010, 10:16 AM   #5
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Ok - I'll try a different one. It's brand new, too. Maybe I'll just switch the fan to a timer and use a double-switch for my main light/shower light. I sure hope that's the problem!
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Old 05-12-2010, 10:18 AM   #6
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FYI: The switch is a "decora" version of this:

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Old 05-12-2010, 10:30 AM   #7
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I've got the same problem, sometimes when I turn off the bath fan, it will trip a gfci that is "downstream" of the switch. I've read other post that say this can happen because of the motor in the fan, causing a small power surge when being turned off, also can happen with ceiling fans. Not sure of the fix, some say that different gfci have slighty different trip points, you could try another one, it might not be quite as sensative.
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Old 05-12-2010, 10:38 AM   #8
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Originally Posted by vtboy51 View Post
I've got the same problem, sometimes when I turn off the bath fan, it will trip a gfci that is "downstream" of the switch.
Do you mean "upstream"?
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Old 05-12-2010, 10:43 AM   #9
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I have my power from the panel entering the light/fan switch box, in that box I'm splicing a feed that goes to power to a gfci outlet on the other side of the bathroom. The fan switch is essentially tied to the LINE side of the gfci.
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Old 05-12-2010, 10:47 AM   #10
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Hmm, my fan is on the load side. How does anything on the line side trip the gfci? A bank teller doesn't know if someone robs you in the parking lot on the way out

I believe you....just don't understand.
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Old 05-12-2010, 11:02 AM   #11
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I've been wiring for 15 years, and never have seen this either. I'm not sure why a surge on the line side would cause it to trip. It's possible that the gfci looks for surges on the load, line, and on the actually plugins (this is considered the load side also) . If someone can better explain, I'd appreciate it.
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Old 05-12-2010, 11:58 AM   #12
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Me too. Fan upstream of GFCI trips...


I have power directly from the panel running into a junction box. In this junction box, I have a double switch like the one picture above, with each switch supplying power to one duct fan. One 14/2 exits this box and supplies four outlets daisy-chained (two wet bar outlets and two entertainment system outlets). The first outlet in the chain is GFCI and will trip when I turn power OFF to either of the fans. It does not trip when I power ON the fan. I think what is happening is that at the moment the fan is powered off, the fan still spins for a while and produces back EMF. Perhaps this is what is tripping the GFCI? If this was a DC fan, the fix would be simple: a 1N4001 diode across the fan terminals. I don't know what the fix would be for AC fans. I'm tempted to try a different GFCI from a different manufacture to see if that changes things as suggested by vtboy51. I need to get this fixed as I will have an entertainment system and a Megatouch game plugged into those outlets downstream of the GFCI.
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Old 05-12-2010, 01:50 PM   #13
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What manufacturer gfci do you have? Mine is a Leviton 15A from home depot. I have some in the house from lowe's - I think cooper. I'll try swapping them.

Also - I think it only trips when flipping the switch slowly.

Maybe a different switch - like a fancy timer switch - would help.
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Old 05-12-2010, 05:07 PM   #14
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Hmmm! I'll recount my experience!

The single incandescent in the laundry area didn't provide enough light. So, I bought a T8 single lamp fixture (with a pull chain switch at HD.
I plugged it into the GFCI in the laundry area and all was fine for about 2 years!
I have been rearranging the location of the laundry receptacles and I hooked up the new wire, in the same manner as it had been connected before.
When I pressed the TEST button the GFCI tripped, but the light stayed on?????
Taking the receptacle apart, I found that the LINE wire were connected to the LOAD terminals.
Connecting them properly, everything seemed to function as required.
However, from time to time, when turning OFF the fixture with its pull chain switch, the GFCI trips!
I have a dehumidifier plugged into the same outlet, its auto start and stop, and it is not a problem.
The GFCI never trips until the flourescent fixture is turned off.
I have yet to open up the fixture, but it does have an electronic ballast (Chinese ?) so I'm wondering if this gives a kick that trips the GFCI!

Last edited by Wildie; 05-12-2010 at 05:09 PM.
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Old 05-13-2010, 10:29 AM   #15
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I plugged it into the GFCI in the laundry area and all was fine for about 2 years!

So it must have been right.

However, from time to time, when turning OFF the fixture with its pull chain switch, the GFCI trips!

So the leakage current is at or slightly below the GFCI tripping threshold?

I have a dehumidifier plugged into the same outlet, its auto start and stop, and it is not a problem.

Could be the cumulative effect of the fixture and this heavy load.

The GFCI never trips until the flourescent fixture is turned off.
I have yet to open up the fixture, but it does have an electronic ballast (Chinese ?) so I'm wondering if this gives a kick that trips the GFCI!


e = -L(di/dt); you should get a huge voltage spike when you interrupt the current in a circuit containing inductance.
Possibly this could be fixed by putting a 400v MOV on the fixture.
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